The present invention relates to a latch needle for a textile machine, including a latch which is pivotal in a longitudinal slot of a needle shank and which is pivotally mounted by means of a continuous bearing bore on a one-piece, cylindrical shaft bolt which is inserted into a corresponding coaxial bore of the needle shank cheeks laterally delimiting the sides of the longitudinal slot and which is fixed in the needle shank cheeks so as to be secure against displacement.
Latch needles of this type are used in various textile machines, particularly in knitting machines, but also, for example, in special sewing machines.
Generally, the latch bearing must meet high demands with respect to mechanical strength and accuracy of the latch guidance, particularly if the latch needle is used in a fast moving knitting machine or for knitting with robust yarns. The wedge effects initiated by the latch during the knitting process which act on the needle shank cheeks delimiting the sides of the longitudinal slot tend to urge the needle shank cheeks apart while, simultaneously, strong leverage forces act on the shaft bolt by way of the latch.
The latch bearing by means of its bearing bore on the smooth cylindrical jacket face of a continuous shaft bolt results in a very accurate and wear resistant latch guidance. Nevertheless, latch needles having such continuous shaft bolts have lost almost all their significance today because they suffer from cheek breakage when subjected to high stresses and particularly when subjected to dynamic stresses. This is so because the end of the shaft bolt is rigidly fixed to the needle shank cheeks, for example, by screwing or welding (see German Patent No. 1,296,734) thus resulting in a rigid latch bearing arrangement which is completely inelastic in the direction transverse to the axis of symmetry of the needle. This has been found to be the cause of premature cheek breakage. Therefore, almost all of the latch needles presently employed in practice are those in which the bearing bore of the needle latch is pivotally seated on two bearing pins pressed out of the material of the needle shank cheeks as disclosed, for example, in U.S. Pat. No. 3,934,109 and British Patent No. 836,297. Due to the unpredictable flow behavior of the material of the needle shank cheeks pressed into the bearing bore, these bearing pins, which have been produced by an embossing process and are connected with the needle shank cheeks, have more or less irregular jacket faces, with the result that the load per unit of surface area of the needle latch on the bearing pin is relatively small even for a needle fresh from the factory.